| 1 | It also has the fastest orbit. | |
| 2 | The earth spins around on its axis as it travels around the sun. | |
| 3 | Well, it's all down to the Earth's orbit around the sun. | |
| 4 | We know there in equation one how to derive the time that it takes to go around. | |
| 5 | It takes the planet only 88 days to whirl around the sun, though, so a Mercurian day lasts about three-quarters of the Mercurian year. |